Loud-speaking telephone receiver



NOV. 16, 1926. 1,607,587

B. A. ENGHOLM LOUD SPEAKING TELEPHONE RECEIVER Filed Jan. 5. 1925 3 Sheets-Sheet 1 Fig-1 lNVENTOR f Ber 'nard AQ Enghalm mff w.

ATTORNEYS Nov. 16, 1926. 1,607,587

, I B. A. ENGHOLM LOUD SPEAKING TELEPHONE RECEIVER Filed Jan. 5. 1925 3 Sheets-Sheet 2 Bernard A. Engholm TORNEYS Nov. 16, 1926. 1,607,587

B. A. E NGHOLM I LOUD SPEAKING TELEPHONE RECEIVER File' Jan. 5. 1925 a Sheets-Sheet 5 INVENTOR Bernard A. Engholm Patented Nov. 16: 1926.

UNITED STATES PATENT OFFICE.

IB ERNARD- A. ENG-HOLM, OF SEATTLE, WASHINGTON, ASSIGNOR TO THE ROLA COM- PANY, OF SEATTLE, WASHINGTON, A CORPORATION OF WASHINGTON.

LOUD-SPEAKING TELEPHONE RECEIVER.

My invention relates to magnetic structures, and to electromagnetic devices formed therewith, more especially designed for use in loud speaking telephone receivers such as are employed in radio communication.

Among the important objects of my invention are, first, the provision of a highly sensitive electromagnetic structure wherein hysteresis and like losses are reduced to the minimum; the provision of a general arrangement of such structures which is cheap and convenient for assembly and for association with other parts to complete the telephone receiver, and in which the several parts lend themselves readily to precision justment as is essential may be readily made, and in general, the simplification and improvement of such magnetic and electromagnetic devices as. are intended for the purpose mentioned, both of themselves and within the unit.

My invention is comprised in the novel magnetic structures and the novel association therewith and therein of electromagnetic devices, as shown in the accompanying drawings, described in the specification and more particularly defined by the claims terminating the same. v

In the accompanying drawings I have illustrated an embodiment of my invention which is its present preferred form.

Figure 1 is an axial sectional view through the assembled device on the line 11 of Figure 2, and Figure 2 is a bottom plan view thereof, the binding posts and support therefor being omitted.

Figure 3 is an exploded viewin perspective, and Figure 4 is an assembly view, likewise in perspective, of the pole tip unit and associated parts.

Figure 5 is an enlarged vertical section throughthe pole tip unit and associated parts, substantially on the line 5-5 of Figure 6, and Figure 6 is a horizontal sectional view through the same unit on the line 66 of'Figure 5. Figure 7 is a detail in perspective showmg the manner of assembling the armature.

In previous devices designed for employment in loud speaking telephone receivers it has been found that the electromagnetic structure was more or less delicate and required exceedingly careful handling to prevent its being thrown out of adjustment or otherwise damaged, Another difliculty in previous devices haslbeen the impossibility, with the construction employed, of making the several parts sufliciently accurate to en able them to fit together perfectly and without adjustment. Where attempts have been made to overcome the latter-difliculty, by providing for adjustment of all parts, the first difficulty has been increased, the large number of adjustments rendering the device delicate, but the lack of precision inherent in the necessary mode of constructing the several parts necessitating a large number of adjustments. i enough for this lack of accuracy which is a necessary evil when employing machined parts, but such adjustments are liable to be improperly made through carelessness, or the parts are liable to be thrown out of ad justment. Such devices are also diflicult to adjust and to assemble.

My device is intended to be built up of units which can be formed by precision machines, as by dies, so that the several parts can be many times more accurately formed and assembled than is possible by forging and finishing similar parts of the same material. By accurately forming the parts their assembly is simplified, and the necessity of adjustment is eliminated.- In my device there is. in fact, only a singleadjustment, to the armature support, and while this also might be eliminated, I prefer to retain it to permit variation of the tone of These compensate well the reproducer. The device is assembled in completeseparable units, in which-all parts are held in definite relationship to each other and in such manner that handling or accidental jarring, and in fact, rather rough usage, will not harm the structure. It also simplifies .the ,iassembly o'fthe entire device and its connection-to the sound reproducing portion of the telephone receiver. MAS a. basis for the entire device I employ a permanent magnet 9 which may be formed nearly circular. Preferably its opposing ends are separated somewhat. This magnet is suitably supported in association with sound reproducing devices such as the diaphragm 8, the diaphragm being supported between the usual resilient rings 80 in a cap 81, the cap bein secured upon. a casing 82 and a horn 83 eing supported. upon the ca It will be understood that these detalls of the sound reproducing device form no essential art of this invention and may be replaced y any that are found suitable. Between the ends of the magnet 9 and preferably toward the center of the ringshaped magnet I position a pole tip unit, bestdllustrated in Figures 3, 4', 5 and 6. This I unit includes two opposingpole tips 1, spacer means such as the non-magnetic bars 2, an

armature 3 supported from the spacer bars and having its ends positioned between the pieces. If, as shown herein, the screws 91 engage the pole tips 1, the screws 91 must.

be of non-magnetic material.

Because of the clamping action of the pole pieces 90 upon the pole tips 1, and also because of the desirability of preventing accidental displacement'ofthe pole tips relative to each other and relative to the arma-' ture 3, it is essential that they be held in definitely spaced relation. It is also desirable to eliminate hysteresis losses and the like, thus increasing the sensitivity and faithfulness of reproduction of the device.

Again, accuracy of the pole tips as a whole,.

the pole tips are bifurcated or U-shaped so that the two legs of each pole tip are positioned opposite like legs of the other pole tip, and the holes 15 and bolts 5 passing through form a means for accurately alining and registering the legs 11 of the pole tips. The through bolts 5 are also secured and P l p a coil coils held Within the "supported in the spacer bars 2, of which two and operatively positioned relative to may be employed the two sh0wn' herethe P P and Such as the in as lying at opposite sides of the pole through bolts 5 m u a ug 0f f tips. Suitable nuts 51 thread upon the bolts elements 111 the P P P 111 d h 5 at each end, by means of which thespacer spaced relatlon, except as Wlll be apparent hereafter. V f r Thispole tip unit, the separate elements d h ld i b1 Of which Will more particularly described a The armature is of special construction,

fi j i held n p i b Pieces It is desirable to provide an armature of sufwhich are essentially clamping devi t ficient mass and so formed that it will not whichserve as magnetic conductors between become saturated but will at all tim r eachend of the magnet 9, and'the c rr main sensitive, yet it is desirable so to supsponding pole tip? "1. These pole pieces 90 port this armature that it will be immediate. are each secured y one end to the opposing ly responsive to electromagnetic im ulses. ends of the magnet 9, as by means of the Also, for the same reasons that the po e tips bolts or screws 92, and their other ends over- 1 a laminated, it i desirable to laminate la Between these overlapping ends of the' the armature 3. Laminating the armature p0 e ieces 90 the pole tipunit 1s positioned, produces another advantage, inthat the and ymeans of clampmg screws 91 passmagnetic flux will enter the; several laminaing through apertured lugs 93. in one pole tions more readily from their edges, and the piece and received in like lugs of the other reluctance of the armature is thus reduced,

pole piece, -the-pole piece may bedrawn down and its saturation point is raised. This may and clamped upon the adjacent pole tips be. assisted by punching the laminations forming part of the pole tip ,unit to establish lengthwise of the grain of the metal. good magnetic contact therewith. 'Also by H For the support of the armature I have properly positioning theslugs 93 of the pole shown a resilient strip 31 which may be suitpieces, as may be done accurately by punchably supported from the spacer bars 2. as, mgout these pieces, the clamping screws '91, for-example, by studs 32 receivable in a hole may be made to lie in contact with the side 23 in the spacer bars. Essentially the studs faces of the pole tip unit, as is best shown in 32 form part of the armature support and Figures 5 and 6, and thus to hold this unit may he connectedrto the ends of the resilient against displacement relative to the pole strip 31 by passing a small key or pin 30 bars and the laminations of the pole tipsmay be drawn together into a single .unit

f throu h registering holes provided in the without decreasing the distance between the II end the stud 32 and strip 31, the end of the stud 32 being shown-as split-to receive the end of the strip 31. By threading the outer ends of the studs 32 where they protrude beyond the spacer bars 2, and by providing an adjusting nut 33 therefor, it is possible also to adjustslightly the angle of thearmature 3 about the axis of the studs 32, and to hold it in adjusted position. It is possible also to adjust the tension in the strip 31, to vary its resistance to movement, and to change the natural period of the armature, and thereby the tone of the reproducer. By twisting one stud in the opposite direction to the other the strip 31 is greatlystiif ened, its initial tension being greatly increased. adjusted position. v

The several laminations of the armature3 may be supported in'the strip31 in any suitable manner so that they are retained in proper position relative to eachother. -As a convenient means of securing this result I have formed the laminations with'a shouldered lug or lugs 34 substantially at their centers and have provided in the strip 31 a longitudinally extending slot through which the ends of the laminations may be passed until the shoulders of the lugs 34 -en-' gage the strip 31. The shoulders then serve as stops for the "individual laminations.-

Preferably these laminations are inserted first from one side of thestrip-31 and next supporting strip 31, yet without increasing to any appreciable degree the movable mass- 7 of the armature and without unbalancing it to any appreciable extent. Two of the laminations, at about the center of the series,'may be slightly prolonged, as indicated at 36, and to these prolongations may be secured in any suitable manner, as by a drop of solder, the connecting link 84- extending to: the diaphragm 8.-

It is desirable to space the ends of the legs 11 of opposing pole tips as little as possible,

for the magnetic reluctance of the air gap varies as the square of the distance between poles. It is not'desirable, however, to cut down the distance through which the end of the armature, interposed ,between these spaced pole tips, may oscillate. By chamfering the ends of the armature, as is indicated at 37 the armature is given an increased dis tance through which it may move without coming. into contact with the poletips, yet

Set .screws 39 hold the studs in unit. For this purpose I have found it desirable to form the spacer bars 2 in the form pole tips; spacer bars 2 and the U-shaped pole tips form a housing Within which the coil 4 is repole tips and the nearest point of the armature, at the inner edge of each leg 11. As the armature approaches the limit of its movement its chamfered end becomes nearly parallel'tb the end plane of the'pole tip, insteifd of presenting a corner which would contact with the poletip. By thus permitting unrestricted'movement of the armaturethe faithfulness of its reproduction is increased. This effect may alsobe assisted by reason of the fact that the'increase in resist ance of the torsional mounting, towards the limits of the armatures movement, is compensated for by the increase in flux through the armature due to the increase in area of surface through which the flux passes readily. The coil, 4 is included within the pole tlp their flanges 21 being alined with the legs 11 of the pole tips and bearing against the outside laminations of each of the two opposin In this manner the channele ceived. This form lends itself readily to precision manufacture, the length of the spacers being determined by definitely spaced tools, and the necessary holes being drilled in it by a gang drill while the channel is held in definitely positioned jigs.

Preferably the coil is divided into two parts, these two parts being held slightly spaced. For this purpose the inner ends of the studs 32. which project slightly through the web of the channeled spacer bars 2, are I shouldered, to provide a reduced portion 38. The two parts'of the coil 4 then are each held between the inner faces of the flanges 21 of the spacer bars and the inner faces of the legs 11 of the pole tips on the one side, and the'reduced portions 38 of the two studs 32 on the other side. They are also formed of a size so that they fit exactly between the bottoms of the U-shaped pole tips 1, and they are provided with central apertures 41 through which the ends of the armature 3 extend. It will be understood that the coils are wound upon nonmagnetic spools ,40, as bakelite. Thus the two coils are definitely held against movement within the housing formed by the two pole tips 1 and the two opposite spacer bars 2 and surrounding the ends of the armature 3 and in such association with the pole tips 1 as to give the maximum effect to fluctuations of the electric impulses in producing movement of the armature.

' spaced relation the laminated poletip's 1,

these pole tips and spacer bars forming a housing within which the two coils 4 are held in definite relationship, substantially immovable, and the spacer bars forming a support whereby the armature 3 maybe held in definite relation to the pole tips andsubstantially enclosed within the pole tip unit so that'it is not liable to be damaged. If

adjustment .of the position of the armature is necessaryihis may be accomplished by varying slightly the angular position of-the studs 32, and if adjustment of the tension of the strip 31 and consequently the degree of movement of the armature 3 is found desirable this may be done by separatin the studs-32 or allowing them to approac by means of adjustment of the nuts 33. Tor-o- 'sional adjustment of one stud against the other-.stiffens the mounting, as has been noted. Outsideof adjust ment, which is intended 'for the convenience of the assembler and tester, it has been found that no further adjustment is desirable or neces sary, parts being accurately formed. For

greater security in maintaining any adjustment of-the armature mounting, I may pro- .vide the set screws 39, engaging the studs 32, as mentioned heretofore. 7 This pole tip unit may be readily handled, and to assemble it into the telephone receiver-it is only necessary to clamp it between the pole pieces 90 clamping screws. 91. In this connection it should be noted that the spacers 2 do not space apart the pole pieces 90, except indirectly.

- They are secured directl to the pole tips 1,

vwhich extend slightly a ove and below the ends of the spacer bars' 2, so that the latter do not contact with either pole piece 90. If after securing the unit between the pole pieces 90 adjustment of the position of the pole tip unit relative to the connecting link 84 is necessary, this may be accomplished prior to final tightening of the clamping screws 91 by adjustment of the pole pieces 90 relative to the securing bolts 92. These bolts 92 may also serve to su ort a non-mag "netic basefi upon which Hiding posts, in-

dicaied at 61, may besupported, these bein electrically connected, as is well understoo to the terminals of the coils 4 and to the lead-in wires (not shown). Thereremains only the connection of the connecting link 8;! to the protruding tip 36 of the armature, which may be accomplished'by means of a drop of solder or any other suitable means. 'Ihus connected the armature and 'its support is under no tension whatsoever,

but is free to be moved in,opposition to."

the torsional resistance of the resilient strip 31 upon passage of suitable electrical impulses through the coils 4.

lVhat I claim as my vinvention is:

1. A magnetic structure comprising a y means of the magnet having its opposing poles dis osed in overlapping relation, two pole ti s t erebetween, means maintainingsaid po e tips in definitely spaced relation, and means for l a definite spaced relation therebetween, two

pole pieces having overlapping ends, their other endsbeing secured to respectively .opposite poles of the magnet, and their over lapping ends each contacting with one of i i said pole tips, andmea'ns for clamping said pole tip unit between the overlapping ends of said pole pieces. f v

4. A magnetic structure comprising. a magnet, a magnet pole tip unit comprising two opposed pole tips and spacer means secured to each of said pole tips to maintain a definite spaced relation therebetween, two pole pieces having overlapping ends, their other ends being secured to respectively oposite poles of the magnet, and their overaptping ends each cont-acting with one of em pole tips, and means for clamping said pole tip unit between the overlapping ends of said pole pieces, said. clamping means comprising a pluralityof screws extending through one ole piece and'threadin into the other, and disposed at op ite si es of and engaging said pole tip unit to maintain it in definite relationship to said pole pieces.

5. A magnet 'pole structure comprising a pair of opposed. pole tips, channel-like non-magnetic spacer bars at opposite sides of said pole tips, said spacer bars being socured directly to each pole tip to maintain the tips in definitely pa'cedrelation and to formItherwit-h a hous1ng.

'6. A magnet structure comprising a pair 'of opposedv laminated pole tips, non-magnetic 'spacer bars at opposite sides of the iii mries of laininations and extending between opposite pole tips to maintain them in definite spaced relation, said bars being recessed between their sides and ends to form a h'ousing, in conjunction with thepole tips, means for maintaining registry of the laminations v i in eachpoletip, and means for securing thespacer members and the laminations of each pole t p together to form a unitary structure. a 7

7. 'A magnet pole structure com rising a pair of opposed bifurcated pole tips, nonmagnetic spacer means disposed at opposite 4 spaced supports,

. structure comprisinga resilient stri sides of the two pole tips, "said spacers in the-extension of the space between the legs of the pole tips, being recessed to form a housing in conjunction with said pole tips, and means for clamping the pole tips between said spacers to form a unitary structure. 1 v

8. A magnet pole structure comprising a pair of laminated pole tips each having registering holes in the several laminations thereof, a non-magnetic spacer bar extending between the two pole tips at opposite sides thereof, said bars being recessed between their sides and ends t6 form a housing, in conjunction with'the pole tips, a clamping bolt extending between said spacer members and through the holes in the laminations of the pole tips to maintain said pole tips in definite spaced relation, and clamping nutsthreaded upon'said bolts for clamping said spacer members and the several laminations of the pole tips into a unitary structure.

9. An armature mounting for an electromagnetic structure comprising' a pair of a stud receivable in each support, a resilient strip extending between said studs, an armature supported in said strip, and means for adjusting the relative positions of said studs.

10. An armature for an; electromagnetic structure comprising a pair of spaced supports, a slotted strip extending between said supports, and a plurality oflaminations extending through said slot in the strip.

11. ,An armature for an electromagnetic structure comprising a pluralit of laminations, anarmature support, an positioning means engageable between the support and each lamination to maintain the several laminations fixed in relationship.

12. An armature for an electromagnetic structure comprising a plurality of laminations each having a shoulder substantially at ,its center, and a slotted supporting strlp therefor, each lamination being inserted through the slot in said strip to contact its shoulder with the stri and adjacent laminations being inserte from opposite sides of the strip.

13. An armature for an electromagnetic structure comprising a resilient strip and a,

plurality of laminations supported therefrom, for oscillatory movement about the axis of said strip.

14. An armature for an electromagnetic plurality of laminations supporte therefrom, a support for each end of said strip, and means for varying the tension in said strip. e

15. An armature for an electromagnetic structure comprising a slotted supporting strip, a plurality of laminations each having shouldered lugs substantially at its center,

and a each lamination being inserted endwise through the slot in said strip to contact the shoulders of said lugs with the strip, adjacent laminations being inserted from opposite sides of the strip, and the interstices between lugs being filled with solder to unite the la'minations and the supporting stri 16. An electromagnetic structure inclu' the ends of said strip being supported pole tips, and means secured in opposite spacers and engaging opposite ends of said resilient strip to support the armature;

18. An electromagnetic structure including a pair of opposed pole tips, non-magnetic spacer means at opposite sides of said pole tips and secured to each pole tip to maintain them in definite spaced relation, an ai-mature, including a transverse resilient supporting strip, positioned between said pole tips, means secured in opposite spacers and engaging opposite ends of said resilient strip to support the armature, and means for adjustirig the angular position of and tension in said strip.

19. An electromagnetic structure compris ing a pair ofbiiur'cated pole tips each having its two legs positioned opposite like legs of the other pole tip, two channeled nonmagnetic spacer bars having the edges of their ch'annels alined and contacting with the legs of the pole tips to form a housing, means connecting said channels and pole tips together to maintain the pole tips in definitely spaced relation, an armature having its ends positioned between the legs of said pole tips and supported between .its

*ends from said spacer bars, and coils within the ,housing formed by said spacer bars and pole tips and operatively positioned relative to said armature.

20. An electromagnetic structure com rising a pairof bifurcated pole tips each aving its two legs ositioned op osite like legs of the other po e tip, two cianneled nonmagnetic spacer bars. having the ed es of their channels alined and contacting with the legs of the pole tips to form ahousing, means connectingsaid channels and pole tips together to maintain the pole ti s in definitel spaced relation, an armature aving its endg positioned between the legs of said pole tips ends positioned between the 1e and supported between its endss from said spacer bars, a pair of coils within the housing formed by said spacer bars and pole t1ps, and each surrounding an end of said armature.

21. An electromagnetic structure comprising a pair of bifurcated pole tips each having its two legs positioned opposite hke legs of the other pole tip, two channeled nonmagnetic spacer bars having the edges of their channels alined and contacting with the legs of the pole tips to form a housing, means connecting said channels and pole tips together to maintain the pole tips in definitely spaced relation, an armature having its of said pole tips and supported between lts ends from said spacer ars, a pair of coils within the housing formed by said spacer bars and pole tips, and each surrounding an end of said armature, and means engaging said coils tov maintain them fixed in osition.

22. An electromagnetlc structure comprising a pair of bifurcated pole tips each havmg its two legs disposed opposite and adjacent to like legs of the other pole tip, two

non-magnetic spacer bars extending between said pole tips at opposite sides thereof, to form therewith a housin means connecting said spacer bars and, sai pole tips to maintain the latter in definitely spaced relation, an armature positioned between said pole tips, armature supporting means extending betweensaid spacer bars, and including a shouldered stud supported in each of said spacer bars, and a coil within said housing at each side of said shouldered studs and operatively positioned relative to said armature, each coil being held between the adj acent legs of both pole tips and the reduced portions of said two shouldered studs.

23. An electromagnetic structure comprising a pair of U-shaped pole tips each having its two legs disposed opposite and adjacent to like legs of the other pole tip, two channeled non-magnetic spacer bars having the edges of their channels alined and contacting with the legs of the pole tips to form a housing, means connecting said spacers and pole tips 'to maintain the latter in definitely spaced relation, an Larmature having its ends disposed between adjacent legs of the two pole tips, armature supporting means extending between the webs of the channeled spacers and including a shouldered stud received in each spacer, and a coil surrounding .each end of the armature within said housing, and maintained definitely fixed in position therein by contact with the bottoms of both U- shaped pole-tips, with the inside of the legs, and with the reduced portions of the armature-supporting studs.

24. An electromagnetic structure comprismg a pair of bifurcated pole tips each having its twolegs positioned opposite like legs of the other pole tip, means for maintaining said pole tips in definitely spaced relation, an armature having its ends positioned between adjacent ends of the two pole tips, means for supporting said armature for movement about a central transverse axis, and a coil operatively positioned relative to said armature, the ends of said armature being chamfered to lie in planes parallel to the planes of the ends of the adjacent pole tip legs at the limits of the armatures vibrations.

25.- An electromagnetic structure comprising a pair of opposing pole tips, a coil positioned in operative relation thereto, an armature positioned between said pole tips, and an armature mounting including a member resisting movement of the armature and characterized by an increasing ratio of resistance towards the ends of the armatures movement from its normal position, said ar- 'mature and the pole tips cooperating therewith being formed to increase the magnetic flux passing therebetween towards'the ends of, the armatures movement to compensate for the disproportionate increase in resistance of said mounting.

26. An electromagnetic structure comprising a pair of opposing pole tipsya coil positioned inoperative relation thereto, an armature having an end positioned between said 7 pole tips, and an armature mounting including a member interposing torsional force to" the movement of said armature from its normal neutral position, the end of said armature being chamfered to approach parallelism with the adjacent ends of said pole tips towards the limits of its movement.

27 Am armature mounting for an electromagnetic structure comprisingpa pair of spaced supports, a stud receivable in each 30. An armature for an electromagnetic structure comprising a plurality of lamina t1ons, an armature support engageable with the several laminations only between their ends, and means interengageable between the support and the laminations to maintain the latter fixed in relationship.

31. An armature for an electromagnetic structure comprising a plurality of laminations each having a shoulder substantially at its center, and a supporting strip engageable with said laminations and with the shoulders thereof to fix the several laminations in position relative to each other.

32. A magnetic structure comprising a magnet having its opposing polesdisposed drawing each magnet pole into intimate conin spaced parallel planes, two pole, tips therebetween, means rigidly maintaining said ole tips in spaced relation, and means for rawing each magnet pole into intimate contact with its respective pole tip.

33. Av magnetic structure comprising a magnet having its opposing poles disposed in spaced parallel planes, two pole tips each comprising a plurality of laminations disposed in planes normal to the planes of the magnet oles, and positioned therebetween, means or maintaining said pole tips in definitely spaced relation, and means for tact with each lamination of its respective pole tip.

34. A magnetic structure comprising a magnethaving its opposing poles disposed inparallel overlapping relation a magnet pole tip unit positioned between said magnet poles, and comprising two opposed pole tips and spacer meansvsecured to each ofsald pole tips to maintain a definite spaced relation therebetween, and means for clamping magnet, a magnet said pole tips between the overlapped poles,

the spacer means being of less extent than "the unit therebetween, and a single screw passing 'through each of said pole fpieces and received in the respective poles 0 the'mag net to connect the pole pieces and pole'tips thereto.

36. An electromagnetic structure compris .ing a pair of opposed pole tips, spacers at opposite sides of said pole tips, each spacer being recessed intermediate its sides and ends, said spacers being secured directly to each pole tip to maintain'the tips .in. definitely spaced relation,'and to. torm therewith a housing, a coil located within said housing, and an armature disposed in operative relation to said coil and pole tips.

37. An armature mounting for an electroma netic structure comprising a pair of spaced supports, a resilient strip extendin between said supports, two means supporte each in one of said supports, and engaging the oppositeentls of said strlp to support it,

an armature supported upon said strip, and means for adjusting the separation of said first pair of means to vary the tension in said strip. 8

An armature mounting ,for an electromagnetic structure comprising a pair of-- spaced supports, a resilient strip extending between said supports, two means supported each in one of said supports, and engaging the opposite ends of said strip to support it an armature supported upon said strip, an means for adjusting the two first means relative to each other to vary the relative angular position of the two ends of the strip.

39. An armature for an electromagnetic. structure comprising a resilient .strip'adapted to be supported by both ends, and a pluas 3 between their ends by the strip between its rality of laminations supportingly engaged ends.

.0. An armature for an electromagnetic structure comprising a plurality of laminations each having a shouldered lug substantially at its center, adjoining lugs having their shoulders oppositely faced and spaced slightly to form a channel extending transversely of the series" 'of laminations, and

means for maintaining said laminations fixed in position comprising a transverse member received in said channel.

41. An armature for an electromagnetic structure comprisinga plurality of laminations each having a shouldered lug substantially at its center, adjoining lugs havin their shoulders oppositely faced and spaced slightly to form a channel extending transversely of the series of laminations, the transverse interstices between lugs being filled with solder to unite the laminations and to complete the channel; and a transverse supporting member received in said channel.

42. An electromagnetic structure comprising a pair of opposed pole tips, non-mag netic spacers at opposite sides of said pole tips secured directly to each pole tip to maintain the tips in definitely spaced relation, a

coil within the space between said pole tips and said spaces, means in said space engaging said coil-to maintain it-fixed in position, and an armaturedisposed in operative relation to said coil and pole tips.

43. An electromagnetic structure comprising a pair of opposed ole tips, non-magnetic spacers at opposite si es of saidpole tips secured directly to each pole tip to maintain the tips in definitely spaced relation, a pair of diametrically opposed shouldered studs,

one received in each of said spacers, a pair of coils within t e space between said pole tlps and said spacers, one of the said coils being 4 positioned at each side of'a line connecting said shouldered studs, and being held between the adjacent legs of both pole tips and the reduced portions of said two shouldered studs, and an armature disposed in operative relation to said coils and pole tips.

l 44. An armature for an electromagnetic struoture-comprising a resilient strip, means for tensioning said strip, and an armature body supported on said strip and projecting at opposite sides thereof.

45. An armature for an electromagnetic structure comprising a resilient strip, means supportingly engaging the opposite ends of said strip, and an armature body secured on said strip intermediate its ends and projecting at opposite sides thereof.

igned at Seattle, King County, Washington, this 13th day of February, 1925.

y BERNARD A. ENGHOLM. 

